1. Field
One embodiment of the invention relates to a wake-up control technique which is suitably applied to a battery-powered personal computer, etc., including a wake-up function of recovering from a power-off status to a power-on status in response to a wake-up signal.
2. Description of the Related Art
In recent years, a battery-powered and easily portable notebook personal computer has become widely used. To maximally secure an operation time period by a battery, a computer of this kind has been contrived so as to save power consumption.
As regards the most basic method for preventing useless power consumption, it is required for power of an unused computer to be frequently turned off. Various kinds of systems which automatically return from the power-off status to the power-on status and enable users to immediately start using the computers without operating power buttons have been proposed in consideration of usability (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2000-3233).
A system which can return the notebook computer being in a display-unit-closed status from the power-off status to the power-on status, for example, only by operating an external mouse connected to a universal serial bus (USB) connector has been referred to as a wake-up function. If the computer does not have this wake-up function, since the computer cannot return from the power-off status to the power-on status without opening the display unit to operate the power button, this wake-up function produces a great effect.
It is required for the wake-up function in the aforementioned example to be configured so that the computer continues power supply to a USB controller which communicates with the external mouse connected to the USB connector also the computer is in a power-off status, and so that the USB controller generates a wake-up signal for operating the wake-up function when data has been received from the external mouse. This configuration is formed in accordance with an instruction from a basic input/output system (BIOS) to which a control tight is transferred from an operation system (OS) when the computer is brought into the power-off status.
Here, it is assumed that the computer is in the power-off status under a situation which enables again supplying the power supply after the power supply has completely shut off without an alternating-current adapter being connected and also with exhaustion or removing of a battery. In this case, since the computer is not configured for the wake-up function based on the instruction from the BIOS, even if the mouse is operated, the computer is not returned from the power-off status to the power-on status.
However, a user is not in a position to distinguish the difference in the two kinds of power-off statuses, a system capable of operating normally the wake-up function is strongly required also in the case assumed as mentioned above.